Published Japanese patent application no. JP 63134020 A describes a ceramic filter element for an exhaust filter in an internal combustion engine that is constructed from a corrugated, spirally wound filter sheet. To manufacture the filter sheet, heat-resistant inorganic fibers in an aqueous suspension are mixed with ceramic powder and processed into a sheet. Several superimposed sheets are rolled into the desired shape of the filter body, so that honeycomb flow paths are formed between adjacent filter sheets. The filter body is subsequently fired at a high temperature.
A disadvantage of this ceramic filter element is that it is relatively costly to manufacture. In a first process step, a filter sheet must first be produced from the suspension of heat resistant inorganic fibers and the raw ceramic powder. This filter sheet must then be processed into the desired filter shape in a second process step and finally fired in a third process step. A further disadvantage is that the inorganic fibers in the finished filter body can reduce the filtering efficiency.
An exhaust gas filter for diesel engines is known from U.S. Pat. No. 4,704,863 (=DE 35 01 182). The ceramic filter bodies disclosed in that document comprise stacked planar and porous filter segments between which gas channels are formed. The gas channels are alternately closed. An exhaust gas stream flowing in on the side where the gas channels are open is forced by the plugs to flow through the porous filter segments, transversely to their faces. The exhaust gas channels on the opposite side are open in the discharge direction and release the filtered exhaust gas stream. This document gives no indication as to how the ceramic filter bodies disclosed therein are manufactured. Structurally comparable bodies, known for example from exhaust gas catalysts, are produced by extrusion. This requires high tooling costs for shaping. The extrusion process limits the degrees of freedom in the shaping of the filter body, particularly the filter segments and the gas channels. A flow-optimized design of the diesel particle filter is difficult to achieve.
US patent publication no. 2007/0186911 A1 (=WO 2006/005668) describes a ceramic exhaust gas filter for internal combustion engines having a filter body formed of ceramic-impregnated paper. A smooth or solid web and a corrugated impregnated paper web each are stacked into a semi-finished product to form gas channels and then rolled up into a wound filter body. The shape of the corrugations of the corrugated paper web is constant over the entire length of the web so that the gas channels also have a constant cross section along their running length.
It is therefore an object of the present invention to provide a ceramic filter element of the aforementioned kind that is simple with regard to its configuration and can be produced inexpensively.